Recovering 3D shape from shading is ill-posed, so to solve the problem the visual system must use assumptions or additional information about the surface material, surface shape, and lighting. We examined whether viewers can infer the lighting properties from the shaded surface of a familiar object and then use that information while judging the shape of an unfamiliar and irregular object in the same scene. Subjects estimated local orientation for points on the unfamiliar test surface by adjusting a gauge figure until it appeared normal to the surface [Koenderink et al. 1992]. We revealed the lighting direction and ratio of directional vs ambient lighting in the scene by rendering a nearby sphere. We manipulated the reliability of this information by varying the reflectance of the sphere. The reference sphere and test surface were rendered as Lambertian surfaces with attached shadows. Observer settings were more accurate when the lighting properties were reliably revealed by the reference sphere, demonstrating that subjects are able to infer the lighting direction and the ratio of directional vs ambient lighting, and then make use of that information. The increase in accuracy was greatest when the light was coming from below and when the reliability of the reference stimulus was high. These data show that observers can use information from the lighting of a familiar object to interpret the shape of an unfamiliar object in the same scene, and that they use a light-from-above prior when lighting information is unreliable.